1. Field of the Technology
The present technology relates to a semiconductor laser device, an optical pickup apparatus, and a method of manufacturing a semiconductor laser device.
2. Description of the Related Art
In recent years, a semiconductor laser device has been often mounted in an optical pickup apparatus for recording and reproducing on an optical recording medium such as a CD (Compact Disk) which uses an infrared wavelength range in the vicinity of 780 nm for recording and reproducing information, a DVD (Digital Versatile Disk) which uses a red color range in the vicinity of 650 nm, and a BD (Blu-ray Disk) which uses a violet-blue wavelength range in the vicinity of 405 nm.
Optical pickup apparatuses corresponding to a number of types of optical recording media may include a plurality of semiconductor laser devices of a single wavelength. However, since the structure of the signal detection light-receiving element for detecting the reflective signal from the corresponding optical system or the optical recording medium is complicated, it is necessary to carry out cumbersome installation calibration procedures a lot of times, and it is difficult to achieve miniaturization.
For this reason, recently, for example, a semiconductor laser device capable of emitting lights of two wavelengths corresponding to the DVD and the CD in a single casing has been developed, and a technique capable of miniaturizing and assembling components of the optical system as an optical pickup apparatus or the signal detection light-receiving element by reducing the number of the elements has been proposed.
First, as a first related art, an optical pickup apparatus disclosed in Japanese Unexamined Patent Publication JP-A 2001-209963 will be described.
FIG. 15 is a simplified cross-section view illustrating a schematic configuration of the semiconductor laser device of the first related art. FIGS. 16A and 16B are simplified cross-sectional views illustrating a schematic configuration of the optical pickup apparatus having the semiconductor laser device of FIG. 15. First, the semiconductor laser device will be described.
The semiconductor laser device includes two light sources emitting two wavelengths composed of a light source X1A having a semiconductor laser element X1 to emit light beam having a wavelength λ1 for DVD, and a light source X1B used to emit light beam having a wavelength λ2 for CD, and a two-wavelength optical deflection element X2 having a birefringent material. The two-wavelength optical deflection element X2 is arranged with a predetermined angle such that a linearly-polarized light beam of the wavelength λ1 entering the two-wavelength optical deflection element X2 serves as ordinary rays, and a linearly-polarized light beam having a wavelength λ2 entering the two-wavelength optical deflection element X2 serves as extraordinary rays. The linearly-polarized light beam having a wavelength λ1 directly transmits through the optical deflection element X2, and the linearly-polarized light beam having a wavelength λ2 is deflected to make those optical axes in alignment with each other. Such a deflection angle is influenced by the gap of the light originating point between the optical source X1A and the light source X1B and the thickness of the optical deflection element X2 having the birefringent material.
Next, the optical pickup apparatus having the aforementioned semiconductor laser device will be described. The light beam of the wavelength λ1 emitted from the light source X1A of the semiconductor laser device is transmitted through the optical deflection element X2 and is collimated through the collimator lens X3 and is condensed by the object lens X4 onto the optical recording medium X5. The light beam having a wavelength λ2 emitted from the light source X1B is deflected by the optical deflection element X2 so that its optical axis is made in alignment with the optical axis of the wavelength λ1, and is then transmitted through the collimator lens X3 and the object lens X4 and is condensed onto the optical recording medium X5 through the same optical path as that of the light source X1A.
Next, as a second related art, the semiconductor laser device disclosed in Japanese Unexamined Patent Publication JP-A 2005-259268 will be described.
FIG. 17 is a simplified cross-sectional view illustrating a schematic configuration of the semiconductor laser device according to the second related art. In the semiconductor laser device of this related art, three semiconductor laser elements having different wavelengths are arranged to be located on a straight line as seen from the light emitting side. When it is assumed that the wavelengths are λ1 (light source X6A), and λ2 (light source X6B), and 23 (light source X6C), they have a relationship λ1<λ2<λ3, the light source X6A of the wavelength λ1 is arranged in the center, the light sources X6B and X6C of the wavelengths λ2 and λ3, respectively, are arranged in both ends with distances d1 and d2, and a diffractive element X7 is arranged perpendicular to the optical axis of the wavelength λ1 at a position away by a distance L in an optical axis direction of the wavelength λ1.
The distances d1 and d2 of the light originating point gap of the light sources X6A to X6C are determined by the wavelengths λ2 and λ3 because the pitch of the diffractive element X7 and the distance L from the light originating point of each semiconductor laser element to the diffractive element X7 are constant. As a result, similar to the first related art, by making the first-order diffracted light beam diffracted by the diffractive element X7 the optical axis of the light beam having a wavelength λ1 in alignment with each other, it is possible to allow the first-order diffracted light beam to pass through the same optical path as that of the collimator lens and the object lens (not shown).
Next, as a third related art, an optical pickup apparatus disclosed in Japanese Unexamined Patent Publication JP-A 2005-327335 will be described.
FIG. 18 is a simplified cross-sectional view illustrating a schematic configuration of the optical pickup apparatus according to the third related art. The optical pickup apparatus according to the third related art includes: semiconductor laser devices X8A and X8B that emits light beams of two different wavelengths λ1 and λ2; a diffractive element X9 that diffracts the light beams of wavelengths λ1 and λ2; a collimator lens X10 for collimating the first-order diffracted light beam diffracted by the diffractive element X9; an object lens X11 for condensing the light beam parallelized by the collimator lens X10 onto an optical recording medium X12; and a signal detection light-receiving element X13 that receives the reflective light beam from the optical recording medium X12.
The diffractive element X9 has a diffractive grating pattern formed as a transmissive hologram on a glass substrate to make the first-order diffracted light beams of the respective wavelength λ1 and λ2 in alignment with each other to be guided to the optical recording medium X12. In addition, an optical thin film and a wavelength plate (not shown) are formed on the glass substrate such that a light beam which is transmitted through the forward path and then reflected by the optical recording medium X12 in the return path is reflected to the signal detection light-receiving element X13.
However, according to the first related art, as described above, the deflection angle by the optical deflection element X2 is influenced by the light originating point gap of the light source X1A and the light source X1B and the thickness of the optical deflection element X2 having the birefringent material. When there is a thickness deviation therein, it is difficult to make the optical axes of the light sources X1A and X1B in alignment with each other. In addition, if two light sources are included in a single semiconductor laser element X1, the influence may be reduced. However, if the two semiconductor laser elements are used, an installation deviation is generated in the light originating point gap or the inclinations of each optical axis so that it is difficult to make the optical axes in alignment with each other. As a result, a position or an intensity distribution of the light spot on a light-receiving surface of the signal detection light-receiving element (not shown) that receives the reflective light beam from the optical recording medium varies, and it is difficult to carry out stable operations as an optical pickup apparatus. In addition, in a case where three or more light sources are used, it is difficult to provide a single optical axis using a single birefringent optical element. Furthermore, the optical path length varies from the light sources X1A and X1B to the light-emitting surface of the optical deflection element X2, and the focus position is deviated on a light-receiving surface of the signal detection light-receiving element (not shown) that receives the reflective light beam from the optical recording medium X5 of the optical pickup apparatus. Therefore, in a case where a servo signal and an information signal are received in a common light-receiving area, a focus deviation is generated, and it is difficult to stably reproduce the signal of the optical recording medium.
In addition, according to the second related art, the incident angles of the light beams of wavelengths λ2 and λ3 to the diffractive element X7 vary depending on installation accuracy of three light sources X6A to X6C, position deviations in the optical axis directions of each light source X6A to X6C, as well as the distances d1 and d2 of the light originating point gap, and it is difficult to make three optical axes diffracted by the diffractive element X7 in alignment with one another. Furthermore, if the position deviation is generated in the optical axis direction of the semiconductor laser element, the focal position of the light beam entering the signal detection light-receiving element (not shown) is deviated, so that the reflective light from the optical recording medium may suffer from a focus deviation, and it may be difficult to stably reproduce the signal of the optical recording medium. Similar to the first related art, if there is an optical path difference to the diffractive element X7 exists between the wavelengths λ2 and λ3, the focal position is deviated in each wavelength on the signal detection light-receiving element. When a servo signal and an information signal are received by a common light-receiving area, a focus deviation may occur, and it may be difficult to stably reproduce the signal of the optical recording medium.
In addition, the light sources X6B and X6C are separated from the light source X6A, and the output directions of the light beams from the light sources X6B and X6C are inclined with a predetermined angle with respect to the diffractive element X7. Therefore, the centers of the intensity distributions for the light sources X6B and X6C are reversely deviated from the center of the intensity distribution of the light source X6A so that the centers of the intensity distributions of the light beams incident onto the light-receiving area of the signal detection light-receiving element (not shown) are different from each other. Therefore, since offsets in different directions are introduced into a radial error signal detected through a push-pull method, and particularly, in the light beams of the wavelengths λ2 and λ3 from the light sources X6B and X6C, respectively, it may be difficult to stably reproduce the signal from the optical recording medium.
In addition, since the light sources X6B and X6C are arranged by interposing the light source X6A therebetween, and the grating shape of the diffractive element X7 is formed to have a grating pattern of a constant period, due to a difference of the incident angle between the main light beam and the peripheral light beam, the diffraction angle differs between the main light beam and the peripheral light beam depending on the incident angle and the wavelength. For example, out of the light beams emitted from the light source X6B, while the light beam entering the point X8 in the center of the diffractive element X7 is diffracted in the Z direction, the diffraction angle φ2C of the light beam entering the point X9 deviated from the point X8 on the light source X6B side by a distance r1 is not bisymmetric with the diffraction angle φ2B of the light beam entering the point X10 deviated from the point X8 on the light source X6A side by a distance r1. As a result, the light beams of the light source X6B and X6C emitted from the object lens of the optical pickup apparatus (not shown) and condensed onto the optical recording medium, are subject to significant aberration with respect to the condensing spot of the center light source X6A so that it may be difficult to stably reproduce a servo signal and an information signal such as from pits or the like on the optical recording medium.
In addition, in the third related art, in a case where a diffractive element including a single kind of grating is irradiated by two light sources having different wavelengths, the diffraction angle of the main light beam may be matched, but the diffraction angle of the peripheral light beam is different as in the second related art described above. Therefore, the condensing spot on the optical recording medium is subject to significant aberration, so that it may be difficult to stably reproduce the servo signal and the information signal such as pits or the like on the optical recording medium. Furthermore, since the diffraction angle of the main light beam is different from the diffraction angle of the peripheral light beam, the condensing position in the optical axis direction is different even in the condensing spot on the signal detection light-receiving element. As a result, a focus deviation is generated with different light sources, and it may be difficult to stably reproduce the signal of the optical recording medium.